Mark Harmon played special agent Leroy Jethro Gibbs for 18 seasons of NCIS before leaving in Season 19. Harmon showed up as Gibbs in the series premiere of the prequel show NCIS: Origins, and appeared in a special Veterans Day crossover episode with the mothership series. In June, we learned that Harmon will return as Gibbs for a season-long arc on the upcoming third season of NCIS: Origins. The original NCIS show will also start airing new episodes on Oct. 6, as will the new spin-off series NCIS: New York. Perhaps the third season of NCIS: Origins can do something similar.